Backup cutting elements on non-concentric reaming tools

ABSTRACT

An apparatus for reaming or enlarging a borehole comprising a bi-center drill bit having backup cutters thereon.

TECHNICAL FIELD

The present invention relates generally to enlarging the diameter of a subterranean borehole, and more specifically to enlarging the borehole below a portion thereof which remains at a lesser diameter. The method and apparatus of the present invention effects such enlargement using a bi-center bit.

BACKGROUND

It is known to employ both eccentric and bi-center bits to enlarge a borehole below a “tight,” or undersized. portion thereof.

An eccentric bit includes a pilot section, above which (as the bit is oriented in the borehole) lies an eccentrically laterally extended or enlarged cutting portion which, when the bit is rotated about its axis, produces an enlarged borehole. An example of an eccentric bit is disclosed in U.S. Pat. Nos. 4,635,738 and 5,957,223.

A bi-center bit assembly employs two longitudinally superimposed bit sections with laterally offset axes. The first axis is the center of the pass-through diameter, that is, the diameter of the smallest borehole the bit will pass through. This axis may be referred to as the pass-through axis. The second axis is the axis of the hole cut as the bit is rotated. This axis may be referred to as the drilling axis. There is usually a first, lower and smaller diameter pilot section employed to commence the drilling and establish the drilling axis. Rotation of the bit remains centered about the drilling axis as the second, upper and larger radius, main, or reamer, bit section extending beyond the pilot bit section diameter to one side of the bit engages the formation to enlarge the borehole. The rotational axis of the bit assembly then rapidly transitions from the pass-through axis to the drilling axis when the full diameter or “gage” borehole is drilled.

Rather than employing a one-piece drilling structure, such as an eccentric bit or a bi-center bit, to enlarge a borehole below a constricted or reduced-diameter segment, it is known to employ an extended bottomhole assembly (extended bi-center assembly) with a pilot bit at the distal end thereof and a reamer assembly some distance above. This arrangement permits the use of any standard bit type, be it a rock bit or a drag bit, as the pilot bit, and the extended nature of the assembly permits greater drillstring flexibility when passing through tight spots in the borehole as well as the opportunity to effectively stabilize the pilot bit so that the pilot hole and the following reamer will take the path intended for the borehole. The assignee of the present invention has designed as reaming structures so-called “reamer wings” which generally comprise a tubular body having a fishing neck with a threaded connection at the top thereof, and a tong die surface at the bottom thereof, also with a threaded connection. The upper mid-portion of the reamer wing includes one or more longitudinally extending blades projecting generally radially outwardly from the tubular body, the outer edges of the blades carrying superabrasive (also termed superhard) cutting elements, commonly termed PDCs (for Polycrystalline Diamond Compacts). The lower mid-portion of the reamer wing may include a stabilizing pad having an arcuate exterior surface the same or slightly smaller than the radius of the pilot hole on the exterior of the tubular body and longitudinally below the blades. The stabilizer pad is characteristically placed on the opposite side of the tubular body with respect to the reamer wing blades so that the reamer wing will ride on the pad due to the resultant force vector generated by the cutting of the blade or blades as the enlarged borehole is cut. U.S. Pat. No. 5,497,842, assigned to the assignee of the present invention and the disclosure of which is incorporated herein for all purposes by this reference, is exemplary of such reamer wing designs. U.S. Pat. No. 5,765,653, also assigned to the assignee of the present invention and the disclosure of which is incorporated in its entirety herein, discloses and claims more recent improvements in reamer wings and bottomhole assemblies for use therewith, particularly as regards stabilizing reamer wings and bottomhole assemblies.

One-piece bi-center bits are more compact, easier to handle for a given hole size, more suitable for directional drilling bottom-hole assemblies (particularly those drilling so-called “short” and “medium” radius non-linear borehole sections), and also less expensive to fabricate than reamer wing assemblies.

Thus, there remains a need for an improved one piece bi-center bit for use in short and medium radius wells.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention are directed to a bi-center bit having backup cutters on the blades thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 comprises a perspective side view of a bi-center bit in accordance with an embodiment herein;

FIG. 2 comprises a face view, or view looking up from the bottom of a borehole, of the cross-sectional configuration and cutter placement of the bit depicted in FIG. 1.

FIG. 3 is a perspective view of a blade having a cutter and a backup cutter located and oriented at substantially 90° from the cutter thereon;

FIG. 4 is a perspective view of a blade having a cutter and a backup cutter located and oriented at substantially 90° from the cutter thereon;

FIG. 5A is a view of a blade of a bi-center bit having a cutter and backup cutter thereon;

FIG. 5B is a side view of a blade of a bi-center bit having a cutter and a backup cutter thereon;

FIG. 5C is a cross-sectional view of a portion of a blade of a bi-center bit showing a backup cutter thereon;

FIG. 5D is a top view of a portion of a blade of a bi-center bit illustrating a cutter having side rake;

FIG. 6A is a view of a cutter set comprising a cutter and multiple backup cutters;

FIG. 6B is a view of a cutter set comprising a cutter and multiple backup cutters;

FIG. 7A is a front view of the cutter set of FIG. 6A, showing cutting face overlap;

FIG. 7B is a view of the cutter set of FIG. 6B showing cutting face overlap;

FIG. 8 is a perspective view of a blade having a row of primary cutters cutters and multiple rows of backup cutters thereon for a bi-center bit; and

FIGS. 9 through 9G are each top views of inline cutter sets of an embodiment of the bi-center bit of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1 of the drawings, the depicted bit is illustrated in its normal drilling orientation for clarity. In an embodiment of the invention, bi-center bit 100 includes a pilot bit section 112 comprising a plurality of blades 118 having superabrasive, preferably polycrystalline diamond compact (PDC) cutters 120 and backup PDC cutters 120′ mounted thereto. Fluid courses 122 extending between blades 118 carry drilling fluid laden with cuttings sheared by cutters 120 and 120′ of blades 118 drilling the pilot borehole into junk slots 124, which extend longitudinally on gage 126 of the bi-center bit 100 between gage pads 128. Gage pads 128 may be provided with a wear-resistant gage surface in the form of tungsten carbide bricks, natural diamonds, diamond-grit impregnated carbide, or a combination thereof, as known in the art. Drilling fluid is introduced into fluid courses 122 from ports 132 on the bit face 130, which may comprise nozzles (see FIG. 2).

Bi-center bit 100 also includes reamer bit section 114 comprising a plurality of blades 140 preferably having PDC cutters 120 and backup PDC cutters 120′ mounted thereto. As can be seen in FIG. 1, blades 140 comprise any suitable number of blades based on the size of the bi-center bit 100 and may be located generally spaced about 90° from each other about the reamer bit section 114. Ports 142 (which, again, may comprise nozzles, located intermediate blades 140, feed drilling fluid into fluid courses 144 located in front of (in the direction of bit rotation) blades 140, to carry away formation cuttings sheared by cutters 120 and 120′ of blades 140 when enlarging the pilot borehole to full gage diameter. Blades 140 include truncated gage pads 146, which may also preferably include a wear-resistant surface of the types previously mentioned. One blade 140 includes an elongated gage pad 146′ thereon.

Bit shank 150, having a threaded pin connection 152, is used to connect bi-center bit 100 to a drill collar or to an output shaft of a downhole motor, as known in the art.

Referring now to FIG. 2 of the drawings, elements of bi-center bit 100 which have been previously described in FIG. 1 are identified by like reference numerals for clarity. As can be seen from FIG. 2, pilot bit section 112 includes four blades 118 thereon, the cutters 120 and backup cutters 120′ have been placed and oriented thereon with the backup cutter 120′ located behind a cutter 120 on the same centerline on a blade 118.

The pockets for the backup cutters 120′ are located aft of the cutter pocket for the cutters 120 so that the backup cutters 120′ do not interfere with the cutters 120. The backup cutters 120′ are underexposed by approximately 0.025 inch in diameter from the cutters 120 along the cutter profile for a blade 118. Additional backup cutters (not shown) may be located behind the backup cutters 120′ having any desired back rake angle therefor, to provide an indication when the bi-center bit 100 becomes under-gage by a desired amount, such as under-gage by 0.200 inch in diameter. If the backup cutters 120′ are positioned to have a 90° back rake angle, a backup cutter such as described in U.S. Pat. No. 6,408,958 may be used by being so oriented and located on a blade 118/140 approximately underexposed by 0.100 inch to provide a decrease in the rate of penetration of the bi-center bit 100 when contacting the formation being drilled. Such a reduction in the rate of penetration of the formation being drilled is an indicator that the bi-center bit 100 is under-gage with respect to the desired diameter of a borehole being formed.

An arrangement of the above-described 90° backrake orientation of backup cutters 120′ on a blade 118/140 is illustrated in FIGS. 3 and 4, wherein each backup cutter 120′ is located behind a cutter 120 on a blade 118/140 at an approximate 90° back rake angle.

If the blades 118/140 have multiple rows of PDC backup cutters 120′/120″ thereon (See FIGS. 9 through 9G for backup cutters 120″) backup cutters 120′ are under exposed approximately 0.025 inch from the cutter 120 in front thereof and have approximately the same back rake angle as the cutter 120 located in front thereof, and the backup cutter 120′/120″ aligns with the cutter 120.

To form the backup cutter pockets in the primary portion of the bi-center bit 100 a flat bottom milling tool cuts the drill bit body by plunging directly into the blade 118/140 and travels along the center line of the cutter 120 located in front thereof. If the bit 100 is a particle matrix type bit formed of sintered tungsten carbide particles in a suitable matrix, the backup cutter pockets in the primary portion of the bit 100 are formed by casing the backup cutter pockets in the bit 100 as well as the pockets for other cutters for the bit 100. Methods of manufacturing the bit 100 as a particle matrix composite bit are set forth in U.S. application Ser. No. 11/272,439, filed Nov. 10, 2005, entitled “Earth-Boring Rotary Drill Bits and Methods of Manufacturing Earth-Boring Bits Having Particle Matrix Composite Bit Bodies, the disclosure of which is incorporated herein in its entirety by reference.

Ports 132, which preferably contain nozzles therein as known in the art, direct drilling fluid as shown by the arrows associated therewith, into fluid courses 122 of bit face 130. Likewise, passages within the bit body feed drilling fluid to ports 142 from a central passage or plenum, which also feeds ports 132.

Pilot bit gage diameter is defined by the gage cutters 120′/120″ at the periphery of bit face 130, and thus corresponds generally to (but is nominally larger than) a circle defined by connecting the radially outer pad surface of gage pads 128 (See FIG. 1).

The backup cutters 120′/120″ in the bit reamer section 114 are located in a manner similar to those of the bit face 130 on blades 118 and have the same or similar respective back rake angles.

The addition of backup cutters 120′, 120″ on the bi-center bit 100 provides an extended reamer blade profile and increased shoulder radius allowing the placement of additional cutters on a blade of the bi-center bit 100, increasing the wear resistance of the bi-center bit 100 in the formation being drilled. Additionally, while the backup cutters 120′/120″ have been located directly behind a cutter 120, if desired, backup cutters 120′ may be somewhat laterally (with respect to the cutter path) offset therefrom while still following in the same kerf of the cutter 120.

Illustrated in FIG. 5A is a partial view of a bi-center bit 100 showing the concept of cutter side rake (side rake) regarding cutters 120, cutter placement (side-side) regarding backup cutters 120′, and cutter size (size). “Side rake” is the angle at which a cutter is oriented relative to its path of travel, a side rake of 0° being achieved when the cutting face of the cutter is facing normal to the path of cutter travel, illustration and further explanation being provided below with respect to FIG. 5D. “Side-side” is the amount of distance between cutters in adjacent cutter rows. “Size” is the cutter size, typically indicated by a cutter's diameter.

FIG. 5B illustrates a partial side view of the bi-center bit 100 of FIG. 1 showing the concepts of back rake (also known as fore and aft rake) regarding cutters/backup cutters 120/120′, relative exposure of cutters 120′ with respect to cutters 120, cutting edge chamfer regarding cutters 120/120′ and spacing between cutters 120 and backup cutters 120′.

FIG. 5C is a cross-sectional view through the center of a cutter/backup cutter 120/120′/120″ positioned on a blade 118/140 of the bi-center bit 100. The cutting direction, or direction of cutter travel due to bit rotation, is represented by the directional arrow 72. The cutter/backup cutter 120/120′/120″ may be mounted on the blades 118/140 in an orientation such that the cutting face of the cutter/backup cutter 120/120′/120″ is oriented at a back rake angle 74 with respect to a line 80. The line 80 may be defined as a line that extends radially outward from the face of the bi-center bit 100 in a direction substantially perpendicular thereto at that location. Additionally or alternatively, the line 80 may be defined as a line that extends radially outward from the face of the bi-center bit 100 in a direction substantially perpendicular to the cutting direction 72. The back rake angle 74 may be measured relative to the line 80, positive angles being measured in the counter clockwise direction, negative angles being measured in the clockwise direction. As known to those of ordinary skill in the art, the effective back rake angle of a cutter, rather than the physical back rake angle, is a function of cutter location from the bit centerline, and the rate of penetration of the bit during drilling.

The cutter/backup cutter 120/120′/120″ is shown in FIG. 5C having a negative back rake angle of approximately 20°, thus exhibiting a “back rake.” In other implementations, the cutter/backup cutter 120/120′/120″ may have a positive back rake angle. In such a configuration, the cutter/backup cutter 120/120′/120″ may be said to have a “forward rake.” By way of example and not limitation, each cutter/backup cutter 120/120′/120″ on the face of the bi-center bit 100 shown in FIG. 1 may, conventionally, have a back rake angle in a range extending from about negative 5° to about negative 30°.

FIG. 5D is an enlarged partial top view of a cutter/backup cutter 120/120′/120″ mounted on a blade 118/140 at the face of the bi-center bit 100 shown in FIG. 1. The cutting direction is represented by the directional arrow 72. The cutter/backup cutter 120/120′/120″ may be mounted on the blade 118/140 in an orientation such that the cutting face of the cutter/backup cutter 120/120′/120″ is oriented substantially perpendicular to the cutting direction 72. In such a configuration, the cutter/backup cutter 120/120′/120″ does not exhibit a side rake angle. The side rake angle of the cutter/backup cutter 120/120′/120″ may be defined as the angle between a line 82, which is oriented substantially perpendicular to the cutting direction 72, and the cutting face of the cutter/backup cutter 120/120′/120′, positive angles being measured in the counter clockwise direction, negative angles being measured in the clockwise direction. In additional embodiments, the cutter/backup cutter 120/120′/120″ may be mounted in the orientation represented by the dashed line 78A. In this configuration, the cutter/backup cutter 120/120′/120″ may have a negative side rake angle 76A. Furthermore, the cutter/backup cutter 120/120′/120″ may be mounted in the orientation represented by the dashed line 78B. In this configuration, the cutter/backup cutter 120/120′/120″ may have a positive side rake angle 76B. By way of example and not limitation, each cutter/backup cutter 120/120′/120″ on the face of the bi-center bit 100 shown in FIG. 1 may have a side rake angle in a range extending from approximately 10° to 60° or, in the alternative, approximately 5° to 75°, although if desired they may have a negative side rake angle of approximately the same range or greater.

Illustrated in FIG. 6A is a cutter set for a blade 118/140 wherein the cutter set is located about a centerline 200 on the blade 118/140. The backup cutters 120′, 120″ are located substantially within the same kerf as cutter 120 along centerline 200 while being laterally offset therefrom. Illustrated in FIG. 6B is a cutter set for a blade 118/140 wherein the cutter set is located about a centerline 200 on the blade 118/140. The backup cutters 120′, 120″ are located within the same kerf as cutter 120 along centerline 200 having no offset therefrom.

Additionally, illustrated in FIG. 7A is a face view of the cutter set of FIG. 6A located on a blade 118/140 wherein the backup cutters 120′, 120″ follow the cutter 120 in the same kerf but are offset both vertically and axially along the centerline of the cutter 120 and have a smaller diameter than that of the cutter 120 and have a lesser exposure. Similarly, illustrated in FIG. 7B is the cutter set of FIG. 6B located on a blade 118/140 wherein the backup cutters 120′/120″ are located on the centerline of the cutter 120 in the same kerf but are vertically offset from the centerline and have a smaller diameter than that of the cutter 120, backup cutter 120′ having a lesser exposure than cutter 120, and backup cutter 120″ having a lesser exposure than backup cutter 120′. The backup cutters 120′, 120″ may be either the same size as cutter 120′ or smaller size than cutter 120, as illustrated, if desired.

Illustrated in FIG. 8 is a blade 118/140 having cutters 120 thereon and multiple rows of backup cutters 120′, 120″ thereon, as may be desired or required.

Illustrated in FIG. 9 is a first example of cutter/backup cutters 120/120′, 120″ of the bi-center bit 100 in a top view representation of an inline cutter set 160 having two side raked backup cutters 120′, 120″. The cutter 120 and the backup cutters 120′, 120″ are spaced from each other any desired distance d. FIG. 9 illustrates a linear representation of a rotational or helical swath, or kerf or rotational path in which the inline cutter set 160 may be oriented upon a bi-center bit 100 (FIG. 1). The inline cutter set 160 includes a cutter 120 and two side raked backup cutters 120′, 120″. The side raked backup cutters 120′, 120″ rotationally follow the cutter 120, and each includes a side rake angle 155 which may be any desired side rake angle to the left of the rotational path, such as approximately 5° to approximately 75°. The side raked cutter 120″ also includes a side rake angle to the right of the rotational path which is in the opposite direction to that of side rake cutter 120′, as illustrated. While two side raked cutters 120′, 120″ are provided in the inline cutter set 160, additional side raked cutters may be provided. While wear flats 156, 157 may develop upon the cutter 120 as it wears, by introducing the side rake angle 155 the side raked cutter 120′, 120″ cut parallel swaths or grooves or rotational paths with the apexes 158, 159, of side rake cutters 120′ and 120″ directing the path of the cuttings generated by the bi-center bit 100. Also, as the wear flats 156, 157 grow upon the cutter 120, the apexes 158, 159 of backup cutters 120′, 120″ are able to more effectively fracture and remove formation material on either side of cutter 120. While the inline cutter set 160 is shown here having zero rake angle for cutter 120 and side rake cutters 120′, 120″, the cutter/backup cutters 120, 120′, 120″ may also include any desired rake angle. While the side rake backup cutter 120′, 120″ is included with an inline cutter set 160, the side rake backup cutter 120′, 120″ may be utilized in any backup cutter set, a multiple backup cutter set, a cutter row, a multiple backup cutter row, a staggered cutter row, and a staggered cutter set in any desired manner.

Illustrated in FIG. 9A, is a top view representation of an inline cutter set 160 having a cutter 120, a backup cutter 120′, and a backup cutter 120″ all having the same centerline on the bi-center bit 100 (FIG. 1) illustrated as the rotational path for the inline cutter set 160, the cutter 120 also has any desired back rake angle, the backup cutter 120′ being smaller in diameter than cutter 120 and having any desired back rake angle, and a back up cutter 120′ being the same diameter as the cutter 120, having any desired back rake angle, and having any desired side rake angle 155 to the left of the direction of the rotational path, such as approximately 10° to 60° or, in the alternative, approximately 5° to 75°, with respect to the rotational path of the inline cutter set 160. The cutter 120 and the backup cutters 120′, 120″ are spaced from each other a distance d on blade 118/140 while being located on the same rotational path. The rotational path in FIG. 9A is a linear representation of a rotational path or swath, or kerf or helical path in which the inline cutter set 160 may be oriented upon bi-center bit 100.

Illustrated in FIG. 9B, is a top view representation of an inline cutter set 160 for the bi-center bit 100 including a cutter 120 and two back raked and side raked backup cutters 120′, 120″, all having the same diameter, any desired back rake angle, and any desired side rake angle. The cutter 120 and backup cutters 120′, 120″ are spaced apart any desired distance d on the blade 128/140. The back up cutters 120′, 120″ have any desired side rake angle 155. The cutter 120 and side rake backup cutters 120, 120″ also have any desired back rake. FIG. 9B is a linear representation of a rotational or helical path in which the inline cutter set 160 may be oriented upon a bi-center bit 100. The back raked and side raked backup cutter 120′ rotationally follows the back raked cutter 120 while back raked and side racked backup cutter 120″ follows backup cutter 120′. The back raked and side raked cutter 120′ includes a side rake angle 155, such as approximately 10° to 60° or, in the alternative, approximately 5° to 75°, to the left of the swath or kerf or the rotational path. While two back raked and side raked backup cutters 120′, 120″ are provided in the inline cutter set 160, additional back raked and side raked backup cutters may be provided.

Illustrated in FIG. 9C, is a top view representation of an inline cutter set 160 for the bi-center bit 100 including a cutter 120 and two back raked and side raked backup cutters 120′, 120″ all having the same diameter, and desired back rake angle, and any desired side rake angle. The cutter 120 and backup cutters 120′, 120″ are spaced apart any desired distance d on the blade 118/140. The back up cutters 120′, 120″ have any desired side rake angle 155 therefore. The cutter 120 and side raked backup cutters 120′, 120″ also have any desired back rake. FIG. 9C is a linear representation of a rotational or helical path in which the inline cutter set 160 may be oriented upon a blade of a bi-center bit 100. The back raked and side raked backup cutter 120″ rotationally follows the back raked cutter 120 while back raked and side racked backup cutter 120″ follows back up cutter 120′. The back raked and side raked cutter 120′ includes a side rake angle 155, such as approximately 10° to 60° or, in the alternative, approximately 5° to 75°, to the right of the swath, or kerf or the rotational path. While two back raked and side raked backup cutters 120′, 120″ are provided in the inline cutter set 160, additional back raked and side raked backup cutters may be provided.

Illustrated in FIG. 9D, is a top view representation of an inline cutter set 160 for the bi-center bit 100 including a back raked cutter 120 and two back raked and side raked backup cutters 120′, 120″, all having the same diameter, any desired back rake angle, and any desired side rake angle. The cutter 120 and backup cutters 120′, 120″ are spaced apart any desired distance d on the blade 118/140. FIG. 9D is a linear representation of a rotational or helical path in which the inline cutter set 160 may be oriented upon a blade 118/140 of a bi-center bit 100. The back raked and side raked backup cutter 120′ rotationally follows the back raked cutter 120 while back raked and side racked backup cutter 120″ follows backup cutter 120′. The back raked and side raked cutters 120′, 120″ include a side rake angle 155, such as approximately 10° to 60° or, in the alternative, approximately 5° to 75°, to the left and right respectively of the swath or kerf or the rotational path. While two back raked and side raked backup cutters 120′, 120″ are provided in the inline cutter set 160, additional back raked and side raked backup cutters may be provided.

Illustrated in FIG. 9E, is a top view representation of an inline cutter set 160 for the bi-center bit 100 having a back raked cutter 120 and two back raked and side raked backup cutters 120′, 120″, with side raked side raked cutters 120′, 120″ having the same direction of the side rake angle being to the left of the rotational path of cutter 120 and being offset a distance D, each about a swath or kerf or rotational path to the left and right of the rotational path of cutter 120, respectively, while generally following in the swath or kerf or rotational path of the cutter 120. The cutter 120 and the backup cutters 120′, 120″ are also spaced a distance d on blade 118/140. Cutter 120 and backup cutters 120′, 120″ having any desired back rake angle, while backup cutters 120′, 120″ additionally have any desired side rake angle of approximately 10° to 60° or, in the alternative, approximately 5° to 75°, on blade 23 of bi-center bit 100. The inline cutter set 160 includes back raked cutter 120 and back raked and side raked backup cutters 120′, 120″. The back raked and side raked backup cutters 120′, 120″ include any desired side rake angles 155, such as approximately 10° to 60° or, in the alternative, approximately 5° to 75°, which are in the same direction to the left.

Illustrated in FIG. 9F, is a top view representation of an inline cutter set 160 for the bi-center bit 100 having a back raked cutter 120 and two back raked and side raked backup cutters 120′, 120″, with back raked and side raked cutters 120′, 120″ having the same direction of the side rake angle being to the right of the rotational path of cutter 120 and being offset a distance D, each about a swath or kerf or rotational path to the left and right of the rotational path of cutter 120, respectively, while generally following in swath or kerf or rotational path of the cutter 120. The cutter 120 and the backup cutters 120′, 120″ are also spaced a distance d on blade 118/140. Cutter 120 and back raked and side raked cutters 120′, 120″ have any desired back rake angle, while backup cutters 120′, 120″ additionally have any desired side rake angle of approximately 10° to 60° or, in the alternative, approximately 5° to 75°, on blade 118/140 of bi-center bit 100. The inline cutter set 160 includes back raked cutter 120 and back raked and side raked backup cutters 120′, 120″. The back raked and side raked backup cutters 120′, 120″ include any desired side rake angles 155, such as approximately 10° to 60° or, in the alternative, approximately 5° to 75°, which are in the same direction to the right of the rotational path.

Illustrated in FIG. 9G, is a top view representation of an inline cutter set 160 for the bi-center bit 100 having a back raked cutter 120 and two back raked and side raked backup cutters 120′, 120″, with side raked cutters 120′, 120″ having opposite side rake angles being to the left (120′) and right (120″) of the rotational path of cutter 120 and being offset a distance D, each about a swath or kerf or rotational path to the left and right of the rotational path of cutter 120, respectively, while generally following in swath or kerf or rotational path of the cutter 120. The cutter 120 and the backup cutters 120′, 120″ are also spaced a distance d on blade 118/140. Cutter 120 and side raked cutters 120′, 120″ have any desired back rake angle, while backup cutters 120′, 120″ additionally have any desired side rake angle of approximately 10° to 60° or, in the alternative, approximately 5° to 75°, on blade 118/140 of bi-center bit 100. The inline cutter set 160 includes back raked cutter 120 and back raked and side raked backup cutters 120′, 120″. The back raked and side raked backup cutters 120′, 120″ include any desired side rake angles 155, such as approximately 10° to 60° or, in the alternative, approximately 5° to 75°, which are directed to the right and left.

While the bi-center bit according to the present invention has been disclosed herein with reference to an illustrated embodiment, those of ordinary skill in the art will understand and appreciate that the invention is not so limited, and that additions, deletions and modifications to the disclosed embodiment may be made without departing from the scope of the invention as hereinafter claimed, and legal equivalents. 

1. A bi-center drill bit for drilling subterranean formations, comprising: a pilot bit section having a longitudinal axis, defining a first gage diameter and carrying a a first cutting structure for rotationally engaging a subterranean formation; and a reamer bit section adjacent the pilot bit section, a portion of the reamer bit section extending radially beyond the first gage diameter along a minor portion of a side periphery of the bi-center drill bit and carrying a second cutting structure on the reamer bit section for rotationally engaging the subterranean formations; and a third cutting structure disposed on at least one of the pilot bit section and the reamer bit section, the third cutting structure being positioned rotationally aft of at least one of the first cutting structure and the second cutting structure.
 2. The bi-center drill bit of claim 1, wherein the pilot bit section comprises a fixed-cutter bit and the first cutting structure comprises at least one superabrasive cutter.
 3. The bi-center drill bit of claim 1, wherein the second cutting structure and the third cutting structure each comprises at least one superabrasive cutter.
 4. The bi-center drill bit of claim 1, wherein the reamer bit section comprises a plurality of substantially radially-extending, circumferentially spaced blades, at least one blade of the plurality of substantially radially extending, circumferentially spaced blades extending radially beyond the first gage diameter.
 5. The bi-center drill bit of claim 1, wherein the pilot bit section includes a face carrying the first cutting structure.
 6. The bi-center drill bit of claim 1, wherein the third cutting structure is disposed on the reamer bit section and positioned rotationally aft of the second cutting structure, wherein the pilot bit section further comprises a fourth backup cutting structure rotationally aft of the first cutting structure for rotationally engaging a subterranean formation and, wherein the reamer bit section further comprises a fifth backup cutting structure rotationally aft of the third cutting structure for rotationally engaging a subterranean formation.
 7. A bi-center drill bit for drilling subterranean formations, comprising: a pilot bit section having a longitudinal axis, defining a first gage diameter and carrying a first cutting structure and a second cutting structure rotationally aft of the first cutting structure thereon for engaging a subterranean formation; and a reamer bit section adjacent the pilot bit section, a portion of the reamer bit section extending radially beyond the first gage diameter along a minor portion of a side periphery of the bi-center drill bit and carrying a third cutting structure and a fourth cutting structure rotationally aft of the third cutting structure on the reamer bit section for engaging the subterranean formations.
 8. The bi-center drill bit of claim 7, wherein the pilot bit section comprises a fixed-cutter.
 9. The bi-center drill bit of claim 7, wherein the first cutting structure and the second cutting structure each comprise a plurality of superabrasive cutters.
 10. The bi-center drill bit of claim 7, wherein the reamer bit section comprises a plurality of substantially radially-extending, circumferentially spaced blades, at least one blade of the plurality of substantially radially extending, circumferentially spaced blades extending radially beyond the first gage diameter.
 11. The bi-center drill bit of claim 7, wherein the pilot bit section includes a face carrying the first cutting structure.
 12. The bi-center drill bit of claim 7, wherein the pilot bit section further comprises a fifth backup cutting structure rotationally aft of the first cutting structure for engaging a subterranean formation and wherein the reamer bit section comprises a sixth backup cutting structure rotationally aft of the third cutting structure for engaging a subterranean formation.
 13. The bi-center drill bit of claim 7, wherein the second cutting structure includes at least one of a back rake angle and a side rake angle.
 14. The bi-center drill bit of claim 7, wherein the fourth cutting structure includes at least one of a back rake angle and a side rake angle.
 15. The bi-center drill bit of claim 7, wherein the second cutting structure and the fourth cutting structure each includes at least one of a back rake angle and a side rake angle.
 16. A bi-center drill bit for drilling subterranean formations, comprising: a pilot drag bit section having a longitudinal axis, defining a first gage diameter and including a body with a face having a first plurality of superabrasive cutters secured thereto and a second plurality of backup superabrasive cutters located rotationally aft of the first plurality of superabrasive cutters and a gage section extending longitudinally from a periphery of the face; and a reamer bit section adjacent the pilot drag bit section including at least one blade extending radially beyond the first gage diameter on one peripheral side portion of the bi-centered drill bit and carrying a third plurality of superabrasive cutters thereon and a fourth plurality of superabrasive cutters thereon located rotationally aft of the third plurality of superabrasive cutters.
 17. The bi-center drill bit of claim 16, wherein the at least one blade comprises a plurality of circumferentially spaced blades.
 18. The bi-center drill bit of claim 16, wherein the gage section includes gage pads.
 19. The bi-center drill bit of claim 18, wherein the gage pads provide a bearing surface area on a portion of the gage section.
 20. The bi-center drill bit of claim 19, wherein the gage pads comprise a plurality of circumferentially spaced, longitudinally elongated gage pads separated by longitudinally extending junk slots. 